Portable radar system

ABSTRACT

A portable, direct distance readout, FM-CW radar especially adapted for small craft use in which relative target distance is measured independent of Doppler effects produced by relative target velocity. An indication may be provided of whether the relative target distance is opening or closing. The invention also includes compensation for modulation nonlinearity errors in the final readout.

United States Patent Mosher May 22, 1973 [5 PORTABLE RADAR SYSTEM2,966,676 12/1960 Fox ..343/14 2.622.241 12/1952 Keizer 1 .343/14 I75 IInventor chard Mmhe" Sudbury' Mass 3,500,403 3/1970 Fuller ..343/14 [73]Assignee: Ki products Company, Inc" 3.054,104 9/1962 Wright et aI..343/14 Sudbury, Mass. Primary Examiner-Benjamin A. Borchelt I22]FlIed: 1971 Assistant ExaminerG. E. Montone A ttorney- Weinganen, Maxham& Schurgin 52 0.5. CI. ..343/14 [57] ABSTRACT {51 Int. Cl ..G0ls 9/24 Aortable, direct distance readout, FM-CW radar [58] Field of Search..343/ 14, 17.5 especially adapted for small craft use in which relativetarget distance is measured independent of Doppler [56] References Citedeffects produced by relative target velocity. An indication may beprovided of whether the relative target UNITED STATES PATENTS distanceis opening or closing. The invention also in- 2,581,847 1/1952Espenchied et a]. ..343 14 dudes compensation mdulatin nonlinearity2,659,878 11/1953 Meeker et a]. ..343/14 rors in the final readout- 13Claims, 4 Drawing Figures f T' I I0 I -20 1.. J I 1 I I 24 26 l I I2 I4f f 30 28 TRIANGLE FM RF 1 MIXER AMP WAVE TRANSMITTER 40 I E 1 l6 9 I 38VAR. TO 1 W AUDIO I 08C. 1 28 I I 1 I W PATENTED 3.735.402

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MULTI- 7' VIBRATOR 8O 84 82 00 To AC CONVERTER |NvENToR RICHARD K.MOSHER ATTORNEYS PORTABLE RADAR SYSTEM FIELD OF THE INVENTION Thisinvention relates to radar systems and in particular to portable directreadout FM-CW radar.

BACKGROUND OF THE INVENTION FM-CW radar systems are well known in theprior art and operate, generally, by varying the frequency of atransmitted microwave radar signal in a linear fashion and detecting theinstantaneous frequency difference between the transmitted and receivedecho signals; the frequency difference providing an indication oftransit time for the transmitted signal from radar antenna to target andback to radar antenna. From this transit time relative target distancemay be calculated.

Typical FM-CW radar systems of the prior art are shown in U.S. Pat. Nos.2,881,422; and 2,451,822. One of the main problems with FM-CW radarsystems of this type is their sensitivity to Doppler effects induced byrelative target velocity causing the resulting beat frequency to show anerror component in addition to the frequency component proportional todistance. While the above US. Pat. No. 2,451,822 has overcome thisdefect by providing for offsetting positive and negative Doppler shifteffects, this has been achieved only through the use of expensive,bulky, and difficult to tune delay networks with a plurality of separateradar transmitting and receivers.

In US. Pat. No. 2,881,422, the rate of change of frequency of thetransmitted radar signal is made sufficiently high so that the resultingbeat frequency be tween the transmitted and received signals is largeand the resulting Doppler frequency error insignificantly small. Oneproblem with such a system, however, is that the high rate of change ofthe transmitted radar signal frequency aggravates other system errorsattributable to switching and nonlinearities in the modulating signal.In addition, accurate use of such a system is limited to relativelyshort distances, such as in aircraft low level altimetry, and isunsatisfactory for use with distances encountered in applications suchas small craft navigation.

To overcome or minimize these problems and to provide small craft userswith satisfactory radar navigation tools has required expensive andelaborate radar signal generation circuitry that provides control overcritical frequency sweep characteristics. This, in conjunction withsignal sources constraints imposed by FCC stability requirements, hasincreased cost beyond the point of practicality for small craft users.

SUMMARY OF THE INVENTION A portable, accurate radar system is providedwith is especially suitable for small craft use in determining relativedistance and bearing of reflective targets up to a few miles distant.The radar system can be hand held and sufficiently requires but fewcomponents, with a result that the cost and size of the system iscompatible with the needs of small craft enthusiasts who otherwise findnavigational radar out of financial reach. A CW radar signal istransmitted by a hand held or other antenna and is frequency modulatedby an efficiently generated triangle wave having a relatively longperiod of approximately one tenth second. The radar echo is heterodynedwith the instantaneously transmitted radar beam to produce a beatfrequency.

Over the course of a cycle of the modulating triangle wave the beatfrequency will vary considerably due to both Doppler effects and radarsignal sweep rate nonlinearities. Two systems are provided to compensatefor the effects of Doppler shift and variations in a radar signalfrequency sweep rate.

According to one scheme, accurate average detection is possible bymanually adjusting the frequency of a separate audio oscillator suchthat average pitch of the beat frequency and audio oscillator appear thesame to the listener. This subjective measurement achieves its accuracyin part through the cooperation of the modulating triangle wave shapeand its frequency. The low triangle wave frequency, furthermore, reducesthe switching transients in the beat frequency due to modulating signalslope reversals.

According to a further system a direct readout of distance is providedby having the beat frequency converted to a constant amplitude unipolarpulse train having a period, which is the same as, or twice the periodof, the beat frequency. The average period of the unipolar pulses isdetected by application of the pulse train to a meter that possessessufficient inertia to provide suitable averaging over the one tenthsecond period of variation to yield an accurate meter readingproportional to target distance.

By averaging the pulses over one or more selected half cycles of themodulating triangle wave and comparing this average to the average takenover one or more full cycles used to indicate distance, an indication ofrelative target motion (closing or opening) is provided.

Radar signal frequency stability requirements of FCC regulations arestrict and cannot usually be maintained by portable power sources, suchas batteries, as they degenerate with age. To provide required stabilityinexpensively, a novel, accurate, and simple voltage regulation systemis provided to insure sufficiently constant voltage supply levelsthroughout the radar system circuitry and to eliminate any error in thebeat frequency attributable to supply voltage variation and batteryaging.

DESCRIPTION OF THE DRAWINGS A more complete understanding of thefeatures and operation of the present invention will be obtained byreference to the following detailed description of a preferredembodiment presented for purposes of illustration and to theaccompanying drawings of which:

FIG. 1 is a partial block and partial schematic diagram of a basicportable radar system;

FIG. 2 is a block diagram of direct distance and relative targetvelocity indicators according to the invention;

FIG. 3 is a partial block and partial schematic diagram of circuitry forproviding the modulating triangle wave used in the invention; and

FIG. 4 is a partial block and partial schematic diagram of a powersupply regulator according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1there is shown in block diagram and partial schematic form a portableFM-CW radar system housed within a container 10 and comprising a source12 of a 10 Hz triangle wave used as an FM modulation for and conductedto an FM-CW transmitter 14 normally operating in the radar frequencyspectrum. Transmitter 14 has its frequency varied in accordance with theamplitude of the triangle wave from the source 12. The resulting FM-CWoutput from the transmitter 14 is applied to a wave separator 16 whichdirects the excitation from transmitter 14 to a portable directionalantenna 18, mounted within container and aimed to direct and receiveradar signals through a transmissive portion 20 of container 10. Echoreflections received by the directional antenna 18 from objects struckby the emitted radar signal are returned to the wave separator 16 wherethey are directed to a mixer 24. There, the received echo radar signalsare multiplied by the instantaneous frequency of the transmitted FM-CWradar signal. The resulting beat frequencies are passed through alow-pass filtering amplifier 26 which selects the lower of the beatfrequencies from the mixer 24 for amplification and application to apair of user headphones 28 through a summer 30.

A further input of the summer 30 is provided from a variable frequencyaudio oscillator 32 having a manually adjusted frequency control 34. Thetriangle wave output of the triangle wave source 12 may be similarly fedthrough a rheostat 38 as a frequency control input into the variablefrequency audio oscillator 32.

As is understood, basic FM-CW radar operation depends upon theproduction of a constant tone beat note from the mixing of thetransmitted and received radar signals. To obtain constancy in thisnote, the frequency of the transmitted radar signal must vary linearlywith time and normally this is achieved with a linear modulation by asweep signal. With completely linear FM modulation, the received radarecho will differ in frequency from the transmitted radar signal by aconstant frequency during each edge of the modulating sweep signal sothat mixing of the received and transmitted signals results in aconstant beat frequency tone, the frequency of which is directlyproportional to the distance between the transmitting radar antenna andthe reflecting target.

In theory this principle works well and in sophisticated, expensiveradar systems where sweep and modulation linearity can be accuratelymaintained through expensive generating circuits the theoreticalfunctioning is achieved.

With less complex and less sophisticated radar transmission andmodulation systems, substantial variation in the beat frequency isproduced even from small linearity variations in the radar signalfrequency sweep rate. A listener, through the earphones 28, hears apronounced wobble in the audio frequency. It has been discovered,however, that despite the effect of this wobble or periodic variation inthe frequency of the audio note produced by the beating of thetransmitted and received radar signal it is possible for the listener tocompare it with the audio frequency note from the variable oscillator32, if the period of the wobble is properly chosen. The radar user canaccurately adjust the frequency of the variable oscillator 32 so thatits frequency appears equal to the average wobbling beat note. Theresulting setting of the control 34 can be calibrated in terms of targetdistance to provide an accurate indication of that distance.

An alternative system providing an improvement can be achieved byeffectively varying the frequency of the audio oscillator 32 in relationto the amplitude of the triangle wave from source 12. Since thefrequency of the beat note from the mixer circuit 24, for a given targetdistance, depends upon the slope of the modulating triangle wave fromsource 12 and since that slope normally varies with the magnitude of thetriangle wave it is possible to slightly vary the frequency output ofthe audio oscillator 32 in accordance with the amplitude of the trianglewave to provide a wobble in the output of oscillator 32 that matches thebeat note wobble. By adjusting, through the resistor 38, the amplitudeof the triangle wave applied to vary the frequency of the audiooscillator 32 its output can be made to wobble to substantially the samedegree as the beat note. With the frequency variations in the beat noteand the output of the audio oscillator 32 more closely matched it iseasier to vary the center frequency of the oscillator 32 to match thecenter frequency of the beat note from circuit 24.

As is known, when the target moves relative to the transmitting antenna18 a Doppler shift is induced in the frequency of the echo radar signalcausing it to change from the frequency of the transmitted signal beforereflection by the target. The result is a change in the beat frequencyfrom the mixer 24 which is proportional to the relative target velocity.With the use of the triangle wave from source 12 having equal positiveand negative slopes for modulating the radar signal, the Doppler shiftchange in the beat frequency will be equal and opposite during oppositeslopes of the triangle wave with the net variation in frequencyaveraging to zero over a full cycle of the triangle wave. It isaccordingly still possible for the listener, using the headphones 28, toadjust the frequency from the variable audio oscillator 32 so that itsfrequency appears to be an average of the frequency of the beat notefrom the circuit 24.

The 10 Hz frequency of the triangle wave from source 12 is both high andlow enough so that the resulting two beat tones produced during Dopplereffects can be independently perceived by the listener and the frequencyof the audio oscillator 32 accurately adjusted at an average of the twobeat tone frequencies. The modulating frequency is also sufficiently lowso that the beat note disturbances produced by slope reversals in themodulating triangle wave are acceptably minimal.

With the target relative velocity such that it is approaching the radarantenna 22 the beat frequency will, depending upon the slope of thetriangle wave, be either higher or lower, and with the target recedingthe opposite change in beat frequency is experienced. A modification maybe added to FIG. 1 in order to detect the direction of the relativetarget velocity. A gate 40 is provided to receive on one input theoutput of the summer 30 and on another input a gating signal from thetriangle wave source 12. The output of the gate 40 is fed to theearphones 28. The gate 40 selectively functions to pass the output ofthe summer 30 to the headphones 28 only during a predetermined slope ofthe triangle wave from source 112.

Gate 40 is first continuously enabled for the listener to adjust thefrequency from the audio oscillator 32 to the apparent average of thehigher and lower portions of the beat note at headphones 28. Thelistener is then able, by causing the gate 40 to provide listening onlyduring one slope of the triangle wave, to determine whether the targetis approaching him or receding from him. This is done by detectingwhether the average beat note during that slope of the triangle wave ishigher or lower than the frequency from oscillator 32.

The block diagram and partial schematic of FIG. 2 shows a portable radarsystem operating in a manner similar to FIG. 1 but, by the inclusion offurther processing electronics, being adapted to give a direct meterindication of distance. A source 44 of a triangle wave modulating signaloutputs a triangle wave to FM modulate a radar transmitter 46 operatingwith a center frequency in the microwave radar range and having itsoutput frequency varied in accordance with the amplitude of the trianglewave. The output of the transmitter 46 is fed to a signal separator 48and thence to a portable hand held radar antenna 50 for transmission ina substantially narrow beam in a direction determined by the operator. Areceived radar echo signal is picked up by the antenna 50 and fedthrough the signal separator 48 to a mixer 52 where the received echo,and the transmitted radar signal are heterodyned to produce a beat note,the beat note is amplified by an amplifier 54 and may be applied to aset of earphones 56. The operation of the circuitry of FIG. 2 up to thispoint is substantially similar to the operation of the radar systemexplained in FIG. 1.

The output of the amplifier 54 is also fed to a high gain limitingamplifier 58 where, by appropriate amplification, it is converted to asquare wave signal having relatively steep rising and fallingcharacteristics. The output of the limiting amplifier S8 is fed to ahigh-pass filter 60 which outputs a series of positive and negativeconstant amplitude pulses corresponding to the rising and falling slopesof the square wave from limiting amplifier 58. A full or half waverectifier 62 receives the train of pulses and outputs a unipolar pulsetrain wherein the pulses of the opposite polarity are either clipped orinverted. The output of the rectifier 62, the unipolar pulse train, isfed to a DC current meter 64 wherein the inertia of the needle movementoperates effectively to continuously average the number of pulses. Thefrequency of the modulating triangle wave is low enough so that themeter 64 can accurately average the higher and lower frequencycomponents in the unipolar signal from rectifier 62 without significanteffects from triangle wave slope reversal disturbances. The trianglewave frequency is high enough so that meter wobble can be sufficientlyeliminated.

Alternatively an averaging circuit 66 is provided to receive the outputof the rectifier 62 and to pass pulses therefrom to a counter 68 duringone or more complete cycles of the triangle wave. Counter 68 displays adigital total proportional or equal to distance depending on theadjustment of circuit parameters.

The effect of averaging over one or more full cycles of the trianglewave from source 44 is to balance and cancel effective variations in thebeat note from mixer 52 produced by both nonlinearities in the radarfrequency sweep rate and Doppler shift effects. With a constant FM radarfrequency deviation and triangle wave period, the Doppler shift will beequal and opposite during opposite slopes of the triangle wave fromsource 44 so that averaging over at least a full period will cancel thechanges in pulse spacing from rectifier 62 attributable to the Dopplereffect. The changes in the pulse spacing from rectifier 62 attributableto nonlinearities in the sweep are also averaged.

In order to determine whether a target is approaching or receding fromthe user a further processing system is employed comprising a rectifier70 receiving the output of the high-pass filter 60 and feeding a gate 72controlled by an input from the source 44. The output of the gate 72 isfed to one input of a differential meter 76 with the other input of thedifferential meter 76 fed from the output of the rectifier 62.

The output of the gate 72 is the pulses from the rectifier 70 during apredetermined slope of the triangle wave while the output of therectifier 62 is the pulses from rectifier 62 over at least a full cycleof the triangle wave. In this manner the difference between the outputsfrom the rectifier 62 and and gate 72 represents the Doppler shift onthe received radar echo signal and the reading of the difierential meter76 therefore represents this Doppler shift. By making the rectifier 62half wave and rectifier 72 full wave, gain compensation is establishedso that the direction in which the meter 76 points can be used as anindication of whether the target is approaching or receding from theuser with the amplitude indicating relative velocity.

Several modifications are possible to the FIG. 2 circuitry to achievethe indicated operation and these modifications include the use ofdifferential meter 76 as both the range and relative velocity indicatorby operating the gate 72 to inhibit all pulses from the rectifier 70during the range measurement. It is also possible to feed the output ofrectifier 62 directly to the gate 72 without a second rectifier 70 byproviding compensating gain elsewhere in the circuit. Finally, the meter64 may be used alone for both range and relative velocity, with gaincompensation, by switching the meter 64 between outputs of rectifier 62and gate 72 and detecting whether the meter reads higher or lower whenreceiving the output of gate 72.

The circuitry of FIG. 2 provides a function similar to that of FIG. 1but with direct readout of distance and relative velocity information.Both circuits are useful over a range of distances up to a few nauticalmiles from as close as several yards.

An inexpensive circuit for producing a sufficiently accurate trianglewave for use in modulating the radar transmitters 14 and 46 is shown inpartial block and partial schematic diagram in FIG. 3. A multivibrator78 provides a saturated 10 Hz square wave which is fed through acoupling capacitor 80 into the base of a grounded emitter NPN transistor82 through a resistor 84. The collector of the transistor 82 isconnected to a regulated source of positive potential 86 through aresistor 88 and is further connected to the base of transistor 82through a parallel combination of a biasing resistor 90 and integratingcapacitor 92. With the high gains presently obtainable in state of theart single transistors, the signal at the collector of transistor 82 isa triangle wave of sufficient linearity for use in the radar systems ofFIGS. 1 and 2 when nonlinearities in that signal are compensated asindicated.

With a radar system adapted for portable use, it is necessary that abattery or similar device be provided to operate the circuitry. Inherentin all batteries is a gradual decrease in voltage as the battery chargediminishes. Such a potential reduction will cause a change in the FMradar signal frequency and frequency deviation rate which decalibratethe radar system. This problem is uniquely overcome by a novel voltageregulator circuit shown in FIG. 4 having economy of components andadapted for use with a portable radar system indicated in FIGS. l-3. Thepositive output of a battery 94 is supplied to the collector of an NPNtransistor 96 and is supplied serially through a diode 98 in the forwarddirection and a resistor 100 to the base of the transistor 96. Aregulating zener diode 102 is connected from the base of transistor 96to the negative, common terminal of the battery 94 and is oriented toprovide reverse, breakdown conduction from the base of transistor 96 tothe common point.

The emitter of transistor 96 is connected and supplies current to aterminal of regulated voltage 104 for operating the radar systemcircuitry of FIGS. 1-3. This volt age will remain constant only as longas the zener current remains constant. However, since the zener currentis supplied from the battery through diode 98 and resistor 102, theamount of current through the zener will drop as the battery voltagedrops. To eliminate this effect the voltage at 104 is also used to feeda transformer coupled saturating type of DC to AC converter 106 and 108which outputs an AC signal proportional to the voltage on the emitter oftransistor 96. This AC signal is boosted in voltage level by atransformer 108 which has an output to a rectification circuit composedof a diode 110 and smoothing capacitor 112. The DC output on thecapacitor 112 is adjusted by the amplification of transformer 108 sothat it exceeds the maximum voltage expected out of the battery 94. Thisvoltage across the capacitor 1 12 is returned to the junction betweenthe diode 98 and resistor 100 where it operates to supply regulatedcurrent to regulating diode 102.

Since the voltage supplied from diode 110 and capacitor l 12 is alwaysgreater than the battery supply voltage, diode 98 becomes reverse biasedand cuts off all current from the battery. Thus, a constant current issupplied to zener 102 and it does not vary in voltage as the batteryvoltage drops with age and the emitter output of transistor 96 willremain essentially constant until the battery voltage drops to thevoltage of this emitter.

Diode 98 is required only when the regulation circuit is initiallyturned on. The diode 98 provides forward conduction from the battery 94to the regulating zener diode 102 so that upon turn on an initial outputis established at the emitter of transistor 96 to start the operation ofthe DC to AC converter 106. Since the DC output from capacitor 112 isalways greater than the output from the emitter of transistor 96, theregulator bootstraps itself up in voltage until the zener 102 turns on.Diode 98 is then turned off and the regulators output voltage remainsconstant, independent of battery age.

It will be appreciated by those skilled in the art that while specificcircuit elements and functional blocks have been indicated to exemplifya system according to the invention, others may be substituted thatprovide similar operation. It is also clear, that while specific valueshave been indicated, particularly with reference to frequencies ofoperation, other frequencies and values can be applied without departingfrom the functional advantages indicated above. It is accordinglyintended to limit the scope of the invention only as specified in thefollowing claims.

What is claimed is:

1. A radar system to provide an operator with an indication of thedistance of remote objects comprising:

means for generating a triangle wave;

means for transmitting a radar signal and for receiving reflections ofsaid transmitted signal from a remote object;

means for FM-CW modulating said radar signal with said triangle wave;means responsive to said transmitted and received radar signals forderiving signals at frequencies representative of the difference betweenthe frequency of the transmitted and received signals;

means for providing as the period of said triangle wave a period whichis long in relation to the duration of switching transients in saidderived signal produced by slope reversals in said triangle wave;

means for developing a signal variable over a range of frequenciessubstantially coextensive with the range of said derived signals;

means for allowing said operator to acoustically monitor said derivedsignals and said developed signals; and

control means for adjusting the frequency of said developed signalwhereby said operator can adjust the frequency of said developed signalas monitored to appear as the average frequency of said derived signaland whereby the setting of said control means provides an indication ofthe distance of said remote object.

2. The system of claim 1 wherein the period of said triangle wave islong relative to the period of audible 30 sound.

3. The radar system of claim 1 wherein said means for generating atriangle wave further includes:

means for generating a square wave; and

a single stage of electronic amplification receiving said square wave ata control input thereof and having negative resistive and capacitivefeedback to said control terminal from a terminal of amplified responseto the signal on said control terminal;

said triangle wave being produced at said terminal of amplifiedresponse.

4. The radar system of claim 1 further including a source of regulatedpower for operating said radar system, said source comprising:

a portable power source providing operating potential which diminisheswith source use;

an active element providing controlled conduction between first andsecond terminals thereof in response to a signal on a third terminalthereof and having said first terminal connected to a terminal of saidportable source;

a DC to AC converter receiving as an input the signal at said secondterminal of said active element and providing as an output an AC signalhaving a peak magnitude substantially higher than the signal level fromsaid portable source;

means for developing a DC signal substantially equal to the peak outputof said DC to AC converter;

means for regulating said developed DC signal at a regulated, lowersignal level and for applying said regulated signal level to the controlterminal of said active element; and

means for conducting a signal from said portable source to said meansfor regulating said developed DC signal whenever said developed DCsignal is at a level less than the level of said portable source;

the second terminal of said active element providing regulated power forthe operation of said radar systurn independent of the past use of saidportable \UUI'CC.

S. The radar system of claim 1 further including means for selectivelyenabling said monitor means during one slope of the triangle wave outputof said generating means.

6. A radar system for providing an indication of the distance of remoteobjects comprising:

means for generating a triangle wave having positive and negativeslopes;

means for transmitting radar signals and for receiving reflections ofsaid radar signals from said remote objects; said transmitted radarsignals having the frequency thereof varied with the level of saidtriangle wave;

means for developing a signal having a frequency representative of theinstantaneous frequency difference between said transmitted and receivedradar signals;

means for providing as the period of said triangle wave a period whichis of substantial duration relative to the duration of switchingtransients in said developed signal resulting from slope reversals insaid triangle wave;

means for amplitude limiting said signal developed at said differencefrequency;

means for high-pass filtering said amplitude limited signal;

means for rectifying said high-pass filtered signal to produce a firsttrain of pulses at a rate representative of said instantaneous frequencydifference; and

means for indicating the average number of said pulses in said firsttrain of pulses during one or more whole cycles of said triangle wave toprovide an indication of the relative distance of said remote objects.

7. The radar system of claim 6 wherein said means for generating atriangle wave comprises:

means for producing a signal which has high and low saturation levelsand which periodically switches from one saturation level to the otherwith an inter val between switching of one half the period of saidtriangle wave;

an active element having first and second terminals of controlledconduction therebetween and a control terminal operative in response tosaid signal with high and low saturation levels to control conductionbetween said terminals of controlled conduction; and

a path of negative resistive and capacitive feedback from one of saidfirst and second terminals to said control terminal;

said triangle wave being produced at one of said first and secondterminals.

8. The radar system of claim 7 further including a source of regulatedpower for operating said radar system. said source comprising:

a portable power source providing operating potential which diminisheswith source use;

an active element providing controlled conduction between first andsecond terminals thereof in response to a signal on a third terminalthereof and having said first terminal connected to a terminal of saidportable source;

a DC to AC converter receiving as an input the signal at said secondterminal of said active element and providing as an output an AC signalhaving a peak magnitude substantially higher than the signal level fromsaid portable source;

means for developing a DC signal substantially equal 'to the peak outputof said DC to AC converter;

means for regulating said developed DC signal at a regulated, lowersignal level and for applying said regulated signal level to the controlterminal of said active element; and

means for conducting a signal from said portable source to said meansfor regulating said developed DC signal whenever said developed DCsignal is at a level less than the level of said portable source;

the second terminal of said active element providing regulated power foroperation of said radar system.

9. The radar system of claim 6 further including a source of regulatedpower for operating said radar system, said source comprising: a

a portable power source providing operating potential which diminisheswith source use;

an active element providing controlled conduction between first andsecond terminals thereof in response to a signal on a third terminalthereof and having said first terminal connected to a terminal of saidportable source;

a DC to AC converter receiving as an input the signal at said secondterminal of said active element and providing as an output an AC signalhaving a peak magnitude substantially higher than the signal level fromsaid portable source;

means for developing a DC signal substantially equal to the peak outputof said DC to AC converter;

means for regulating said developed DC signal at a regulated, lowersignal level and for applying said regulated signal level to the controlterminal of said active element; and

means for conducting a signal from said portable source to said meansfor regulating said developed DC signal whenever said developed DCsignal is at a level less than the level of said portable source;

the second terminal of said active element providing regulated power forthe operation of said radar systern.

10. The radar system of claim 6 further comprising:

means for developing a second train of pulses representative of saidinstantaneous frequency difference during one of said slopes of saidtriangle wave; and

means for comparing the average number of said pulses in said firsttrain with the average number of said pulses in said second train toprovide an indication of the relative velocity of said remote objects.

11. The radar system of claim 6 further including means for providingacoustical monitoring of said developed signal.

12. A radar system for providing an operator with an indication of thedistance of remote objects comprismg:

means for producing a fixed repetition rate slightly nonlinear sweepsignal;

means for transmitting radar signals and for receiving reflections ofsaid radar signals from said remote objects;

the frequency of said transmitted radar signals being controlled inresponse to the level of said sweep adjustable means operative with saidgenerating 15 means for automatically varying the frequency of saidgenerated signals in response to the level of said sweep signal; and

means for permitting said operator to compare the frequency of saiddeveloped signals with the frequency of said generated signals wherebythe frequency of the signal from said generating means may be adjustedfor minimum apparent variation from the frequency of said developedsignals and whereby the indicated adjustment of the frequency of saidgenerating means provides an indication of the distance of said remoteobjects;

said adjustable means for automatically varying the frequency of saidgenerated signals further including means operative to provide avariation in the frequency of said generated signals which may beadjusted to substantially match the variation of said developed signalsattributable to the nonlinean'ties in the variation of the frequency ofsaid transmitted radar signals with time.

13. The radar system of claim 12 further comprising means for permittingsaid operator to compare the frequency of said developed signals withthe frequency of said generated signals during selected portions of asingle slope of said sweep signal whereby said operator obtains anindication of the relative velocity of said remote object.

NITE STATES IATENT OFFICE CERTIFICATE OF CORRECTION Patent o. 5 402Datea y 22, 19.73

Inventor-( 4 K. MOSher It -is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

, ABSTRACT, line 8, "final readout" should read -'-final distancereadout".

Column 1 .lir1e 54', "provided with is" should read provided which is--A sighed" and sealed this 10th clay of December 1974.

- (SEAL) Attest: I

McCOY I i, sIBsoN JR. I I c. MARSHALL DANN Attestlog Off cer vCommissioner of Patents USCOMM-DC 60376-P69 FORM PO-105O (10-69) I g"-5. GOVEININT PRIN ING OFFICE I!!! 0-3..33

. v UNITED STATES PATENT OFFICE Q CERTIFICATE OF CORRECTION Patent no.3, 5,402 Datea May 22, 1973 lnventofls) Richard K. Mosher ror appears inthe above identified" patent y corrected as shown below:

It'is certifiedthat er and that said Letters Patent are hereb -ABSTRACT,line 8, "final readout" should read -'-final distance readout".

Columu 1, 11. 54', "provided with is" should read -pro.vided which is--sighed and sealed this 10th day of December 1974.

(SEAL) N Attest McCOY M. GIBSON JR. Arresting Officer C. MARSHALL DANNCommissioner of Patents USCOMMDC 60376-P69 a .5. GOVERNMENT IRIII'HNGOFFICE I!!! O-Jl-lib

1. A radar system to provide an operator with an indication of thedistance of remote objects comprising: means for generating a trianglewave; means for transmitting a radar signal and for receivingreflections of said transmitted signal from a remote object; means forFM-CW modulating said radar signal with said triangle wave; meansresponsive to said transmitted and received radar signals for derivingsignals at frequencies representative of the difference between thefrequency of the transmitted and received signals; means for providingas the period of said triangle wave a period which is long in relationto the duration of switching transients in said derived signal producedby slope reversals in said triangle wave; means for developing a signalvariable over a range of frequencies substantially coextensive with therange of said derived signals; means for allowing said operator toacoustically monitor said derived signals and said developed signals;and control means for adjusting the frequency of said developed signalwhereby said operator can adjust the frequency of said developed signalas monitored to appear as the average frequency of said derived signaland whereby the setting of said control means provides an indication ofthe distance of said remote object.
 2. The system of claim 1 wherein theperiod of said triangle wave is long relative to the period of audiblesound.
 3. The radar system of claim 1 wherein said means for generatinga triangle wave further includes: means for generating a square wave;and a single stage of electronic amplification receiving said squarewave at a control input thereof and having negative resistive andcapacitive feedback to said control terminal from a terminal ofamplified response to the signal on said control terminal; said trianglewave being produced at said terminal of amplified response.
 4. The radarsystem of claim 1 further including a source of regulated power foroperating said radar system, said source comprising: a portable powersource providing operating potential which diminishes with source use;an active element providing controlled conduction between first andsecond terminals thereof in response to a signal on a third terminalthereof and having said first terminal connected to a terminal of saidportable source; a DC to AC converter receiving as an input the signalat said second terminal of said active element and providing as anoutput an AC signal having a peak magnitude substantially higher thanthe signal level from said portable source; means for developing a DCsignal substantially equal to the peak output of said DC to ACconverter; means for regulating said developed DC signal at a regulated,lower signal level and for applying said regulated signal level to thecontrol terminal of said active element; and means for conducting asignal from said portable source to said means for regulating saiddeveloped DC signal whenever said developed DC signal is at a level lessthan the level of said portable source; the second terminal of saidactive element providing regulated power for the operation of said radarsystem independent of the past use of said portable source.
 5. The radarsystem of claim 1 further including means for selectively enabling saidmonitor means during one slope of the triangle wave output of saidgenerating means.
 6. A radar system for providing an indication of thedistance of remote objects comprising: means for generating a trianglewave having positive and negative slopes; means for transmitting radarsignals and for receiving reflections of said radar signals from saidremote objects; said transmitted radar signals having the frequencythereof varied with the level of said triangle wave; means fordeveloping a signal having a frequency representative of theinstantaneous frequency difference between said transmitted and receivedradar signals; means for providing as the period of said triangle wave aperiod which is of substantial duration relative to the duration ofswitching transients in said developed signal resulting from slopereversals in said triangle wave; means for amplitude limiting saidsignal developed at said difference frequency; means for high-passfiltering said amplitude limited signal; means for rectifying saidhigh-pass filtered signal to produce a first train of pulses at a raterepresentative of said instantaneous frequency difference; and means forindicating the average number of said pulses in said first train ofpulses during one or more whole cycles of said triangle wave to providean indication of the relative distance of said remote objects.
 7. Theradar system of claim 6 wherein said means for generating a trianglewave comprises: means for producing a signal which has high and lowsaturation levels and which periodically switches from one saturationlevel to the other with an interval between switching of one half theperiod of said triangle wave; an active element having first and secondterminals of controlled conduction therebetween and a control terminaloperative in response to said signal with high and low saturation levelsto control conduction between said terminals of controlled conduction;and a path of negative resistive and capacitive feedback from one ofsaid first and second terminals to said control terminal; said trianglewave being produced at one of said first and second terminals.
 8. Theradar system of claim 7 further including a source of regulated powerfor operating said radar system, said source comprising: a portablepower source providing operating potential which diminishes with sourceuse; an active element providing controlled conduction between first andsecond terminals thereof in response to a signal on a third terminalthereof and having said first terminal connected to a terminal of saidportable source; a DC to AC converter receiving as an input the signalat said second terminal of said active element and providing as anoutput an AC signal having a peak magnitude substantially higher thanthe signal level from said portable source; means for developing a DCsignal substantially equal to the peak output of said DC to ACconverter; means for regulating said developed DC signal at a regulated,lower signal level and for applying said regulated signal level to thecontrol terminal of said active element; and means for conducting asignal from said portable source to said means for regulating saiddeveloped DC signal whenever said developed DC signal is at a level lessthan the level of said portable source; the second terminal of saidactive element providing regulated power for operation of said radarsystem.
 9. The radar system of claim 6 further including a source ofregulated power for operating said radar system, said source comprising:a portable power source providIng operating potential which diminisheswith source use; an active element providing controlled conductionbetween first and second terminals thereof in response to a signal on athird terminal thereof and having said first terminal connected to aterminal of said portable source; a DC to AC converter receiving as aninput the signal at said second terminal of said active element andproviding as an output an AC signal having a peak magnitudesubstantially higher than the signal level from said portable source;means for developing a DC signal substantially equal to the peak outputof said DC to AC converter; means for regulating said developed DCsignal at a regulated, lower signal level and for applying saidregulated signal level to the control terminal of said active element;and means for conducting a signal from said portable source to saidmeans for regulating said developed DC signal whenever said developed DCsignal is at a level less than the level of said portable source; thesecond terminal of said active element providing regulated power for theoperation of said radar system.
 10. The radar system of claim 6 furthercomprising: means for developing a second train of pulses representativeof said instantaneous frequency difference during one of said slopes ofsaid triangle wave; and means for comparing the average number of saidpulses in said first train with the average number of said pulses insaid second train to provide an indication of the relative velocity ofsaid remote objects.
 11. The radar system of claim 6 further includingmeans for providing acoustical monitoring of said developed signal. 12.A radar system for providing an operator with an indication of thedistance of remote objects comprising: means for producing a fixedrepetition rate slightly nonlinear sweep signal; means for transmittingradar signals and for receiving reflections of said radar signals fromsaid remote objects; the frequency of said transmitted radar signalsbeing controlled in response to the level of said sweep signal toprovide a transmitted signal frequency varying nonlinearly with time;means for developing signals at frequencies representative of theinstantaneous difference in frequency between said transmitted andreceived radar signals; means for generating signals at frequencieswithin a range of selectable frequencies substantially coextensive withthe expected range of said difference frequencies; means for manuallyadjusting the frequency of said generating means within said range ofselectable frequencies, said adjusting means providing an indication ofits setting; adjustable means operative with said generating means forautomatically varying the frequency of said generated signals inresponse to the level of said sweep signal; and means for permittingsaid operator to compare the frequency of said developed signals withthe frequency of said generated signals whereby the frequency of thesignal from said generating means may be adjusted for minimum apparentvariation from the frequency of said developed signals and whereby theindicated adjustment of the frequency of said generating means providesan indication of the distance of said remote objects; said adjustablemeans for automatically varying the frequency of said generated signalsfurther including means operative to provide a variation in thefrequency of said generated signals which may be adjusted tosubstantially match the variation of said developed signals attributableto the nonlinearities in the variation of the frequency of saidtransmitted radar signals with time.
 13. The radar system of claim 12further comprising means for permitting said operator to compare thefrequency of said developed signals with the frequency of said generatedsignals during selected portions of a single slope of said sweep signalwhereby said operator obtains an indication of the relative velocity ofsaId remote object.